1. Field of the Invention
The present invention generally relates to voltage/current reference systems, and more particularly to a layout of a bandgap reference system.
2. Description of the Prior Art
A voltage reference system is an electronic circuit that generates a fixed voltage regardless of the loading on the circuit. A bandgap reference (BGR) circuit is a voltage reference circuit for generating a fixed reference voltage that has a value equal to the electron bandgap level of silicon (approximately 1.2 volts) and that changes very little with temperature. Bandgap reference circuits are widely used in electronic systems, such as the source driver for a liquid crystal display (LCD).
FIG. 1 shows schematically the layout of a bandgap reference circuit 10, among others, in a conventional mixed analog-digital system 1, which also includes at least one high-voltage subsystem 12 and low-voltage subsystems 14A and 14B. According to the conventional layout shown in FIG. 1, the bandgap reference circuit 10 is laid out in the middle, for example, between the low-voltage subsystems 14A and 14B, for the sake of layout symmetry.
As modern integrated circuits become more complex in design and even more enormous in size, noise becomes a non-negligible issue, which affects either the output reference voltage or current of the bandgap reference circuit 10. FIG. 2 schematically illustrates the noise influence on the bandgap reference circuit 10 in the system 1. A noise source 120 originating from the high-voltage subsystem 12 and adjacent to the bandgap reference circuit 10 affects the bandgap reference circuit 10 with noise along various courses 120A and 120B of influence (e.g., west and east courses in the figure). Subsequently, the influenced bandgap reference circuit 10 distributes the noise-added reference voltage/current to the low-voltage subsystems 14A and 14B in the directions 122A and 122B, causing the low-voltage subsystems 14A and 14B to malfunction.
For reasons including that of the conventional bandgap reference circuit not effectively defending itself against noise, a need has arisen to propose a novel bandgap reference system and layout to minimize the noise influence on the bandgap reference system and to prevent the noise from being distributed.